BOERUM HILL - Police have arrested a man they believe intentionally set a fire that injured a family of four children and their grandmother at an apartment in the Wyckoff Garden houses.

Authorities say Thaddeus Boone, 22, of Newark, N.J., set the fire Sunday night after an argument with his girlfriend in her Boerum Hill home. The flames left a 5-month-old boy and his 8-year-old sister in critical condition. Their conditions have since been upgraded to stable.

The incident also left two other siblings and their 63­-year-old grandmother with minor injuries.

Boone has been charged with attempted murder, assault, burglary and arson.